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Carpometacarpal arthritis of the thumb – rhizarthrosis


Key joint of the thumb

Saddle-shaped joint

Biconcavo-convex shape

Joint compression force = 12kg (120kg for strong grip)

3 Main ligamentous stabilisers:

1. Volar or Beak ligament

  • most NB ligament - primary static stabiliser
  • very strong
  • prevents dorsal translation of the MC in key pinch
  • Allows rotational motion
  • Evolutionary remnant of the bony palmar beak
  • synonyms = volar oblique lig., anterior oblique lig.(AOL), volar CMC lig., deep ulnar lig.
  • Important in Bennett's Fractures

2. Dorsal ligament

  • thin & reinforced by APL

3. Lateral ligament

  • broad band running from lateral surface of trapezium to 1st MC base



Described by Pelligrini (1991) following examination of cadaveric & surgical specimens.

Attritional changes in the beak lig. leads to destabilisation of the 1st CMCJ causing degenerative changes.

These changes initially occur in the palmar contact areas of the joint.


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